Patent GB-692721-A (GB)
Title: Improvements in or relating to electrical remote control and supervisory systems
Inventor: GARFIELD WILLIAM LITTERY
IPC: G01S1/02
Filed: 1950-07-24
Abstract: 692,721. Electric control systems. STANDARD TELEPHONES & CABLES, Ltd. July 20, 1951 [July 24, 1950]. No. 18411/50. Class 40 (i). In an electrical remote control system a master station comprises a plurality of oscillators of frequencies F<SP>1</SP>, F', F', ... &c. paired with oscillators of frequencies f<SP>1</SP>, f<SP>2</SP>, f<SP>3</SP>, ... &c. at a slave station such that F<SP>1</SP>-f<SP>1</SP> =F<SP>2</SP>-f<SP>2</SP>=F<SP>3</SP>-f<SP>3</SP>= ... &c. Each oscillator serves both as a source of signal energy for transmission and as a beating oscillator for signal energy received from its paired oscillator. The invention is described as applied to the control and supervision of a normally unattended G.C.A. radar station from a central station over a radio link. Control station, Fig. 1, Transmission. A number of frequency stabilized oscillators 1A ... 6A of different frequencies F', F<SP>2</SP>, ... F<SP>6</SP>, are selected in pairs according to the control function required by respective manually operated controls which momentarily operate switching devices such as 7, 8, 9, 10 to connect the selected pair of oscillators to frequency modulate a carrier in 'a radio transmitter 11 which radiates through a directional aerial 12. Slave station, Fig. 2, Reception. The transmitted wave is received at 13 and after demodulation in receiver 14 is fed through a selector 15 which passes all frequencies in the band covered by the oscillators 1A ... 6A to mixers 16, 21, in parallel. These mixers are also fed from respective oscillators 1B ... 6B, the frequencies of which f<SP>1</SP>, f<SP>2</SP>, ... f<SP>6</SP> are such that the oscillator pairs 1A, 1B, 2A, 2B, ... &c. all give the same beat frequency e.g. 1 k.c/s. This beat frequency will therefore appear only in the two mixers corresponding to the operative pair of oscillators 1A ... 6A selected at the control station. For example if control switch 8 at the control station is operated, the selected pair of oscillators 2A, 3A modulate the transmitter 11 and only the mixers 17, 18 corresponding to oscillators 2A, 3A and 2B, 3B will produce the required beat frequency, whereupon, of the relays 22 ... 27 all tuned to be operated at the beat frequency 23, 24 will be selectively operated, contacts thereof in the contact unit 28 effecting the required control. The controls are of the "lock-on, lock-off type i.e. they lock in the position " on " or "off" to which they have been operated until reception of a further control signal pulse to reverse their position. In the case of e.g. a potentiometer shaft to be set, two control switches such as 9, 10 may be used, successive actuations of one control stepping the potentiometer in a forward direction and the other control serving to reverse the stepping. Slave station. Supervisory signal transmission and reception. Supervisory switches, e.g. 33, 34, 35 are adapted to switch output from associated pairs of the oscillators 1B ... 5B in turn over an electronic or other distributer 36a and a gating switch 37 to frequency modulate the carrier of a radiotransmitter 38 radiating towards the control station by a directional aerial 39. For telemetering, a sender 40 keys the output of oscillator 6B to send pulse trains at a frequency proportional to the amplitude of the quantity being metered, ten pulses/sec corresponding to zero reading and 40 pulses/sec to full scale reading. These telemetering pulses are applied over the gating switch 37 together with the complex signals from the distributer 36a to the transmitter 38. At the control station the transmission is demodulated in the receiver 42 and applied over the selector 43 to all the mixers 44-49 in parallel, which are fed also from the respective oscillators 1A ... 6A, and function to actuate the supervisory indicators 50, 51, 52 in a manner similar to the actuation of the relays 22- 27 of the slave station. The telemetering receiver 53 fed from mixer 49 produces a current of amplitude proportional to the rate of the pulse trains received which is indicated on a meter. Radar information transmission from slave station and reception. The gating switch 37, Fig. 2, is time controlled over line 54a from the radar equipment 54 and functions electronically to connect the radar equipment 54 over line 55 to the transmitter 38 alternately with the terminal 36 for intervals of 148 Á-secs i.e. one-half the radar pulse transmission repetition period. This gating has no effect on 'the response of the indicating arrangements for supervisory and telemetering signals sent over terminal 36. The:radar signals are obtained directly from the receiver 42, Fig. 1, and led to the display equipment 56 through a 6m.c/s rejector 57 to prevent interference from a telephone circuit superimposed on the radio link. Telephony. A 6m.c/s sub-carrier oscillator 58 at the slave station is amplitude modulated by speech signals from microphone 59, the modulated sub-carrier being applied together with the radar and supervisory signals to frequency modulate the output of the transmitter 38. At the control station the telephony sub-carrier is demodulated at 60 and fed to a telephone receiver 61. For communication in the reverse direction, input to a microphone 62, Fig. 1, after amplification at 63, frequencymodulates the output of transmitter 11. At the slave station Fig. 2 the speech output from receiver 14 is fed to a telephone receiver 65 over a low pass filter 64. Modifications. The oscillator outputs may be combined in threes or higher numbers to increase the number of control functions and direct transmission e.g. over a wave guide may be used in lieu of radio transmission.